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Tue, 7 Jul 2026 10:01:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id IowEHH7OTGqNYAAAD6G6ig (envelope-from ); Tue, 07 Jul 2026 10:01:34 +0000 Date: Tue, 7 Jul 2026 11:01:32 +0100 From: Pedro Falcato To: Leon Hwang Cc: linux-mm@kvack.org, Jonathan Corbet , Shuah Khan , Andrew Morton , "Liam R . Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Nathan Chancellor , Peter Zijlstra , Miguel Ojeda , Nicolas Schier , Thomas Gleixner , Thomas =?utf-8?Q?Wei=C3=9Fschuh?= , Alice Ryhl , Douglas Anderson , Gary Guo , Anand Moon , Randy Dunlap , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH] mm/mseal: fix mseal documentation for 32-bit kernels Message-ID: References: <20260703022507.187457-1-leon.hwang@linux.dev> <8f75dc18-dd4c-4989-a76c-eec6cc513ccf@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8f75dc18-dd4c-4989-a76c-eec6cc513ccf@linux.dev> X-Spam-Flag: NO X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWELVE(0.00)[27]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RLtb8czmhwiphoi1fghn1johzr)]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[kvack.org,lwn.net,linuxfoundation.org,linux-foundation.org,infradead.org,kernel.org,google.com,dabbelt.com,eecs.berkeley.edu,ghiti.fr,linutronix.de,chromium.org,garyguo.net,gmail.com,vger.kernel.org,lists.infradead.org]; TAGGED_RCPT(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[linux.dev:email,imap1.dmz-prg2.suse.org:helo,pedro-suse.lan:mid] X-Spam-Level: X-Spam-Score: -2.80 On Fri, Jul 03, 2026 at 10:50:29PM +0800, Leon Hwang wrote: > On 2026/7/3 17:44, Pedro Falcato wrote: > > On Fri, Jul 03, 2026 at 10:25:07AM +0800, Leon Hwang wrote: > >> mseal.o is built only for 64-bit kernels, so 32-bit kernels fall back > >> to sys_ni_syscall() and return -ENOSYS rather than -EPERM. > >> > >> Document the -EINTR return from mmap_write_lock_killable(), fix the > >> CONFIG_MSEAL_SYSTEM_MAPPINGS typo, and describe system mappings in > >> terms of VM_SEALED_SYSMAP. > >> > >> Signed-off-by: Leon Hwang > >> --- > >> Documentation/userspace-api/mseal.rst | 18 ++++++++++-------- > >> init/Kconfig | 2 +- > >> mm/mseal.c | 4 ++-- > >> 3 files changed, 13 insertions(+), 11 deletions(-) > >> > >> diff --git a/Documentation/userspace-api/mseal.rst b/Documentation/userspace-api/mseal.rst > >> index ea9b11a0bd89..1f1cf206670c 100644 > >> --- a/Documentation/userspace-api/mseal.rst > >> +++ b/Documentation/userspace-api/mseal.rst > >> @@ -50,8 +50,10 @@ mseal syscall signature > >> * The start address (``addr``) is not allocated. > >> * The end address (``addr`` + ``len``) is not allocated. > >> * A gap (unallocated memory) between start and end address. > >> - - **-EPERM**: > >> - * sealing is supported only on 64-bit CPUs, 32-bit is not supported. > >> + - **-EINTR**: > >> + * Interrupted while waiting for the mmap write lock. > >> + - **-ENOSYS**: > >> + * The kernel does not implement ``mseal()``. > >> > >> **Note about error return**: > >> - For above error cases, users can expect the given memory range is > > > > Honestly, this whole thing needs to be deleted. We need a proper manpage. > > $ man mseal > No manual entry for mseal > > When searching "mseal manual" using Google, this doc is the first entry. > > So, this change is worthy. Yes, I agree. To be clear, my main gripe is with the current state of things, not your patch. > > > > >> @@ -62,7 +64,8 @@ mseal syscall signature > >> memory range could happen. However, those cases should be rare. > >> > >> **Architecture support**: > >> - mseal only works on 64-bit CPUs, not 32-bit CPUs. > >> + mseal is built only for 64-bit kernels. 32-bit kernels return > >> + ``-ENOSYS``. > > > > This LGTM. > > > >> > >> **Idempotent**: > >> users can call mseal multiple times. mseal on an already sealed memory > >> @@ -131,20 +134,19 @@ Use cases > >> - Chrome browser: protect some security sensitive data structures. > >> > >> - System mappings: > >> - The system mappings are created by the kernel and includes vdso, vvar, > >> + The system mappings are created by the kernel and include vdso, vvar, > >> vvar_vclock, vectors (arm compat-mode), sigpage (arm compat-mode), uprobes. > >> > >> Those system mappings are readonly only or execute only, memory sealing can > >> - protect them from ever changing to writable or unmmap/remapped as different > >> + protect them from ever changing to writable or unmapped/remapped as different > >> attributes. This is useful to mitigate memory corruption issues where a > >> corrupted pointer is passed to a memory management system. > > > > Also LGTM. > > > >> > >> If supported by an architecture (CONFIG_ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS), > >> - the CONFIG_MSEAL_SYSTEM_MAPPINGS seals all system mappings of this > >> - architecture. > >> + CONFIG_MSEAL_SYSTEM_MAPPINGS seals mappings marked with VM_SEALED_SYSMAP. > > > > VM_SEALED_SYSMAP isn't meaningful to userspace. > > > Got it. Will drop this change. > > > > >> > >> The following architectures currently support this feature: x86-64, arm64, > >> - loongarch and s390. > >> + loongarch, riscv, and s390. > > > > This is also useless, every 64-bit architecture will support this. > > > Do you mean dropping this sentence, or this change? This sentence (this is not architecture specific...). > > > > >> > >> WARNING: This feature breaks programs which rely on relocating > >> or unmapping system mappings. Known broken software at the time > >> diff --git a/init/Kconfig b/init/Kconfig > >> index 5230d4879b1c..12bb39f637b1 100644 > >> --- a/init/Kconfig > >> +++ b/init/Kconfig > >> @@ -2112,7 +2112,7 @@ config ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS > >> from a kernel perspective. > >> > >> After the architecture enables this, a distribution can set > >> - CONFIG_MSEAL_SYSTEM_MAPPING to manage access to the feature. > >> + CONFIG_MSEAL_SYSTEM_MAPPINGS to manage access to the feature. > >> > >> For complete descriptions of memory sealing, please see > >> Documentation/userspace-api/mseal.rst > >> diff --git a/mm/mseal.c b/mm/mseal.c > >> index 9781647483d1..0464c7b94ab9 100644 > >> --- a/mm/mseal.c > >> +++ b/mm/mseal.c > >> @@ -132,8 +132,8 @@ static int mseal_apply(struct mm_struct *mm, > >> * addr is not a valid address (not allocated). > >> * end (start + len) is not a valid address. > >> * a gap (unallocated memory) between start and end. > >> - * -EPERM: > >> - * - In 32 bit architecture, sealing is not supported. > >> + * -EINTR: > >> + * interrupted while waiting for the mmap write lock. > >> * Note: > >> * user can call mseal(2) multiple times, adding a seal on an > >> * already sealed memory is a no-action (no error). > > > > And this whole header needs to be deleted as well. No one's looking at > > kernel code for documentation (and if they are, we did a horrendous job > > at actually documenting the thing). > > > > Just to confirm, do you mean removing the entire function comment above > do_mseal()? Yes. Again, not your fault, just old gripes :) -- Pedro